1. Field of the Invention
The present invention relates generally to the control of electronic devices and more particularly to a control arrangement and method that controls the conductive state of an electronic device such that the normal state is conductive and a predetermined control signal is required to render the power electronics device nonconductive.
2. Discussion of the Related Art
Various electronic systems are known where devices are controlled between conductive and nonconductive states. In power electronic systems arranged as source-transfer switches, continuous power to a load is supplied by transferring the supply of the load from one source to another when undesirable characteristics are sensed in the source currently supplying the load. For example, the arrangement in U.S. Pat. No. 5,808,378 provides desirable control features for the solid-state switches that are selectively rendered conductive to supply current to a load from one of two or more sources. Undesirable current flow between sources is avoided and transfer delays are minimized. In U.S. Pat. Nos. 5,644,175 and 5,814,904, when a transfer is desired, current through the conducting solid-state switch is sensed twice before signals are removed from the conducting switch and applied to another solid-state switch to provide current through an alternate source. The arrangement in U.S. Pat. No. 4,811,163 provides solid-state switches across the main power contacts of automatic bus transfer equipment. The solid-state switch is rendered conductive before its respective main contact is closed and a timer circuit maintains the solid-state switch conductive for a predetermined time period selected to ensure that the main contact will be closed while the solid-state switch is still conductive.
The controls for the power electronic devices utilized in these systems are subject to noise that may effect the conducting state of the switch by erroneously turning it on or off. Thus, while these arrangements may be useful and generally satisfactory for their intended purposes, they are prone to erroneously changing the conductive state of switches.
Accordingly it is a principal object of the present invention to provide a control arrangement for electronic devices in which an electronic switch is maintained in a conducting state at all times other than when it is desired to render the electronic switch nonconducting.
It is another object to provide a control method and arrangement to control the conducting status of a power electronic switch via a latched control signal, such that the appropriate receipt of a secure, complex signal is required to change the conducting state of the power electronic switch.
It is a further object of the present invention to latch the conductive state of a switch and toggle the latch to render the switch nonconductive via the decoding of a complex encoded momentary signal.
It is yet another object of the present invention to provide a control that maintains a power electronic switch in a conducting state at all times other than when an active signal is received to turn off the power electronic switch.
These and other objects of the present invention are efficiently achieved by a control arrangement for electronic devices in which an electronic switch is maintained in a conducting state at all times other than when it is desired to render the electronic switch nonconducting. In a specific embodiment, a latched control signal is utilized which is changed by the receipt of a momentary signal to change the conducting state of the electronic switch. For example, according to one specific arrangement, the momentary signal is a secure, complex signal such that appropriate decoding and detection of the proper signal is required to change the conducting state of the electronic switch.